docs: def timestr_mod24(timestr: str) -> int:
      """
      Given a GTFS HH:MM:SS time string, return a timestring in the same
      format but with the hours taken modulo 24.
      """
      try:
          hours, mins, secs = [int(x) for x in timestr.split(":")]
          hours %= 24
          result = f"{hours:02d}:{mins:02d}:{secs:02d}"
      except:
          result = None
      return result